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We present a mechanism for emission of electromagnetic terahertz waves by simulation. High Tc superconductors form naturally stacked Josephson junctions. When an external current and a magnetic field are applied to the sample, fluxon flow induces voltage. The voltage creates oscillating current through the Josephson effect and the current excites the Josephson plasma. The sample works as a cavity, and the input energy is stored in a form of standing wave of the Josephson plasma. A part of the energy is emitted as terahertz waves.PACS numbers: 74.50.+r, 74.25.Gz, 85.25.Cp Continuous coherent terahertz waves have various applications in scientific field such as biology and information science. One of the hurdles for technological advancements in the terahertz region of electromagnetic wave is the development of sources for intense and continuous coherent terahertz waves. Therefore, we investigate a new mechanism for emitting intense continuous and frequency tunable terahertz waves. In the high temperature superconductors, the strongly superconducting CuO 2 layers and insulating layers are alternatively stacked along the c-axis of the crystals and form a naturally multi-connected Josephson junction called intrinsic Josephson junction (IJJ). In the IJJ there appears a new excitation wave called Josephson plasma, the frequency of which is in the range of terahertz 1,2 . The frequency appears in the region inside the superconducting energy gap and the Landau damping is very weak, and thus the excited plasma decays by emitting a terahertz electromagnetic wave.For investigating an emission mechanism of terahertz electromagnetic wave from the IJJ, we use the following model shown by Figure 1. In Fig. 1 the IJJ is shown in green and the electrodes of a normal metal (for example gold) are shown in yellow. An external magnetic field B applied in the direction of the y-axis induces fluxons in the direction. The centers of fluxons are in the insulating layers. In this system, the superconducting and normal currents almost uniformly flow in the direction indicated by J in Fig.1. The fluxons flow in the direction of the x-axis with a velocity v and induce the flow voltage in the direction of the z-axis. These voltages creates the oscillating Josephson current along the z-axis by the Josephson effect, when temperature is low enough below T c and the superconducting current is smaller than the superconducting depairing current along the c-axis. This oscillating current interacts strongly with the Josephson plasma due to the nonlinear nature of the system and intensively excites the Josephson plasma wave as shown later. We use Bi 2 Sr 2 CaCu 2 O 8+δ that is appropriate in the experiments, and apply a magnetic field and external currents around J c the critical current to the IJJ. Then, the frequency of the plasma waves appears in the terahertz frequency range. The plasma wave is converted to an intense terahertz electromagnetic wave in the waveguide (dielectric) shown in orange in Fig. 1.In accordance with the mechanism mention...

Our new molecular dynamics (MD) simulation program, MODYLAS, is a general-purpose program appropriate for very large physical, chemical, and biological systems. It is equipped with most standard MD techniques. Long-range forces are evaluated rigorously by the fast multipole method (FMM) without using the fast Fourier transform (FFT). Several new methods have also been developed for extremely fine-grained parallelism of the MD calculation. The virtually buffering-free methods for communications and arithmetic operations, the minimal communication latency algorithm, and the parallel bucket-relay communication algorithm for the upper-level multipole moments in the FMM realize excellent scalability. The methods for blockwise arithmetic operations avoid data reload, attaining very small cache miss rates. Benchmark tests for MODYLAS using 65 536 nodes of the K-computer showed that the overall calculation time per MD step including communications is as short as about 5 ms for a 10 million-atom system; that is, 35 ns of simulation time can be computed per day. The program enables investigations of large-scale real systems such as viruses, liposomes, assemblies of proteins and micelles, and polymers.

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Silicon nanowires are potentially useful in next-generation field-effect transistors, and it is important to clarify the electron states of silicon nanowires to know the behavior of new devices. Computer simulations are promising tools for calculating electron states. Real-space density functional theory (RSDFT) code performs first-principles electronic structure calculations. To obtain higher performance, we applied various optimization techniques to the code: multi-level parallelization, load balance management, sub-mesh/torus allocation, and a message-passing interface library tuned for the K computer. We measured and evaluated the performance of the modified RSDFT code on the K computer. A 5.48 petaflops (PFLOPS) sustained performance was measured for an iteration of a self-consistent field calculation for a 107,292-atom Si nanowire simulation using 82,944 compute nodes, which is 51.67% of the K computer's peak performance of 10.62 PFLOPS. This scale of simulation enables analysis of the behavior of a silicon nanowire with a diameter of 10-20 nm.

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In this paper, we address high performance extreme-scale molecular dynamics (MD) algorithm in the GENESIS software to perform cellular-scale molecular dynamics (MD) simulations with more than 100,000 CPU cores. It includes (1) the new algorithm of real-space nonbonded interactions maximizing the performance on ARM CPU architecture, (2) reciprocal-space nonbonded interactions minimizing communicational cost, (3) accurate temperature/pressure evaluations that allows a large time step, and (4) effective parallel file inputs/outputs (I/O) for MD simulations of extremely huge systems. The largest system that contains 1.6 billion atoms was simulated using MD with a performance of 8.30 ns/day on Fugaku supercomputer. It extends the available size and time of MD simulations to answer unresolved questions of biomacromolecules in a living cell.

This paper presents a new heroic computing method for unstructured, low-order, finite-element, implicit nonlinear wave simulation: 1.97 PFLOPS (18.6% of peak) was attained on the full K computer when solving a 1.08T degrees-of-freedom (DOF) and 0.270T-element problem. This is 40.1 times more DOF and elements, a 2.68-fold improvement in peak performance, and 3.67 times faster in time-to-solution compared to the SC14 Gordon Bell finalist's state-ofthe-art simulation. The method scales up to the full K computer with 663,552 CPU cores with 96.6% sizeup efficiency, enabling solving of a 1.08T DOF problem in 29.7 s per time step. Using such heroic computing, we solved a practical problem involving an area 23.7 times larger than the state-of-the-art, and conducted a comprehensive earthquake simulation by combining earthquake wave propagation analysis and evacuation analysis. Application at such scale is a groundbreaking accomplishment and is expected to change the quality of earthquake disaster estimation and contribute to society. Categories: Time-to-solution, Scalability, Peak performance I. CONTRIBUTIONS OF SUPERCOMPUTERS TO REDUCING EARTHQUAKE DISASTERS A. Overview and importance of the problem An earthquake can affect many people. The 2011 Tohoku Earthquake in Japan killed 20,000 and more than 200,000 people are still in temporary housing. The loss of lives, damage to the economy, and catastrophic damage are fresh in our memory. This damage occurred in Japan, a country that leads the world in earthquake disaster mitigation, and there are concerns over similar disasters in earthquake-prone mega-cities such as Los Angeles, San Francisco, and Tokyo. Reliable earthquake disaster estimation plays an important role in mitigating such disasters. Physics-based comprehensive earthquake simulation is the only way to make reliable estimations of such infrequent and untestable events, and is